The number of vaccines being developed in novel cell substrates has increased in recent years, but there are concerns about the possible presence of potential contaminants in these substrates. This interagency agreement was initiated to support the development of assays and animal models to better characterize novel cell substrates. Specific activities supported by the contract include the development of assays and standards for detection of unknown and/or latent viruses;assessment of the oncogenicity of cellular DNA;assessment of the potential of cell substrates to propagate TSE agents;and the development of a rapid and reliable assay for the detection of mycolplasma and other contaminating bacteria.